1. Field of the Invention
This invention relates generally to a floppy disc device and, more in particular, to a floppy disc device having a read/write head, a pair of erase heads spaced apart from the read/write head and a delay mechanism for delaying the drivement of the erase heads with respect to the drivement of the read/write head.
2. Description of the Prior Art
A floppy disc device is a contact type recording and reproducing device, in which use is made of a soft thin disc contained within a cover jacket for recording bits of information thereon. Such a floppy disc device is advantageous since random access may be carried out, thereby reducing access time.
In some of prior art floppy disc devices, use was made of a magnetic head assembly with a read/write head and a pair of erase heads arranged without a gap-to-gap distance therebetween. Here, the gap-to-gap distance is defined as a distance between a read/write gap of the read/write head and an erase gap of each of the erase heads in the direction of movement of a recording medium with respect to the head assembly. Such a magnetic head assembly having no gap-to-gap distance is difficult to manufacture and, therefore, expensive to make. Moreover, since the read/write head and the erase heads are all arranged on the same line, they must be operated at the same time, which, in turn, raises a problem of cross coupling between the read/write and erase heads.
In order to avoid such cross coupling, the erase heads may be located spaced apart from the read/write head in the downstream direction with respect to the movement of a recording medium, thereby defining a finite gap-to-gap distance between the read/write and erase gaps. However, in the case of a floppy disc device, a floppy disc usually has a particular recording format as shown in FIG. 1. For example, positions of recording tracks on the surface of a floppy disc are previously determined. Typically, a floppy disc has 77 circular recording tracks, all different in diameter and arranged concentrically with track number 00 allocated to the outermost track and track number 76 to the innermost track. And, each track is comprised of a preamble section, a plurality of sector sections and a postamble section. Sector sections in one track are of the same length and each sector section includes an ID field, containing address information, and a data field, each of which is followed by an individual gap.
As a result, when the erase heads are located as spaced apart from the read/write head to avoid cross coupling in a floppy disc device, criticalness in timing of actuating the erase heads arises. Because, while the gap-to-gap distance remains unchanged, the recording tracks are shorter for inner ones, so are the gaps between the fields. Therefore, the relativity between the gap-to-gap distance of the head assembly and the field gap of the recording track changes from track to track, so that there is a likelihood of over-erasing and/or under-erasing if the timing of actuating the erase heads is not appropriate. In severe cases, the information contained in the ID section could be erased, thereby losing a part of address information.